BEARINGS Berichtzusammenfassung

Bleed systems decrease pressure and temperature in aircrafts to levels acceptable for downstream pipes and air cooling systems. Bleed valves that regulate the pressure determine the aircraft safety and regulate the passengers and crews comfort. Their failures have an impact on flight delay and traffic management, as well as severe economic consequences on airlines.

Today bearings design and material have reached their limit; nevertheless, this technology will remain in use in the next 20 years, thus any issues have to be solved. In this context, the BEARINGS project aimed to propose innovative materials and adapted processes, as well as novel bearings designs through the improved understanding of the encountered degradations using recent advances in contact modelling. The major systems that were addressed by the project were the bleed system and the Auxiliary power unit (APU).

The consortium implemented a top down approach and consisted of six partners representing the industry, research institutions and academia. The project was structured in five technical and one managerial Work package (WP), which were interrelated and undertook the following activities:

1. Analysis and generic requirements definition, which concluded that the wear mechanism responsible for the rapid deterioration of the bearing surface consisted of a combination of factors, such as corrosion, oxide spalling, surface and subsurface initiated fatigue by fracture and carbides. Where sensitisation by grinding and severe oxidation and corrosion did not occur in the raceway void and crack formation was thought as the main contribution to wear. Oxidation of the surface was defined as a contributing but less severe factor. 2. Modelling and computation. In this WP simulation models were developed and executed with the aim to test WP1 assumptions and scenarios. The observed stress levels at the boundaries of the contact justified the local plastic deformation and thus the wear scenario proposed by WP1. Moreover, the designed test bench showed satisfactory reproduction of the contact stresses and degradation mode on the samples. 3. Tribological materials definition and transfer on samples. Inputs from WP1 and WP2 were translated into materials properties requirements and the processes to be adopted in plasma spraying and consolidation of engineered nano-powders were selected. In addition, the proposed materials for bulk and coating were designed, optimised, manufactured and characterised. A manufacturing system was elaborated and all powder systems were developed. 4. Tribological tests and analyses, which included the selection of materials for the friction part in contact with WP3 selected samples, implementation of tribological tests for all samples and selection of suitable friction parts to be transferred on complete ball bearings. 5. Design and manufacturing. During this last stage the proposed technologies were transferred to actual bearing prototypes. New manufacturing processes were investigated in order to produce bearing parts, and complete manufacturing routes were developed for each transferred material and coating solution. 6. Management, which ensured the efficient coordination and monitoring of the activities, as well as the information exchange between the WPs.